Light-emitting element failure detector and method for detecting light-emitting element failure

Abstract

A light emitting element failure detector ( 4 ) includes a light emitting element ( 1 ), a constant current circuit ( 2 ) which supplies an electric current to the light emitting element ( 1 ), and an electric discharge path which discharges an electric charge such as the light emitting element ( 1 ). A light emitting element failure detector ( 4 ) further includes an instantaneous current interruption circuit ( 5 ) which instantaneously interrupts an electric current to the light emitting element ( 1 ) by a current supply path different from the electric discharge path, a diode ( 60 ), a DC power supply ( 61 ), and a current detector ( 62 ). The DC power supply ( 61 ) generates a direct-current reference voltage having a positive value lower than a voltage between the anode and cathode of the light emitting element ( 1 ) in a normal state. The DC power supply ( 61 ), the diode ( 60 ), and the current detector ( 62 ) which are connected in series constitute a parallel electric path of the light emitting element ( 1 ). An anode of the DC power supply ( 61 ) and a cathode of the diode ( 60 ) are arranged on the anode side of the light emitting element ( 1 ). The current detector ( 62 ) detects an electric current which flows in the parallel electric path when an electric current is instantaneously interrupted.

The invention claimed is: 
     
       1. A light emitting element failure detector that detects a short-circuit of a light emitting element in a light emitting element circuit that includes the light emitting element, a current supply path that supplies a current causing the light emitting element to emit light, a constant current circuit that supplies an electric current to the light emitting element via the current supply path, and an electric discharge path that discharges an electric charge accumulated at the light emitting element and at a region connected between both electrodes of the light emitting element when the constant current circuit stops a current supply to the light emitting element, the light emitting element failure detector comprising:
 an instantaneous current interruption circuit that is arranged on the current supply path different from the electric discharge path and that instantaneously interrupts an electric current that the constant current circuit supplies to the light emitting element, and 
 a parallel electric path connected to the light emitting element in parallel between an anode and cathode of the light emitting element, the parallel electric path being different from the current supply path and from the electric discharge path, wherein 
 the parallel electric path comprises
 a diode, 
 a DC power supply that generates a direct current reference voltage having a positive value lower than a voltage between the anode and cathode of the light emitting element in a normal state, in which the direct current reference voltage is applied to the light emitting element via the diode, and 
 a current detector, wherein 
 
 in the parallel electric path, the diode, the DC power supply, and the current detector are connected to one another in series, and the diode and the DC power supply are connected to each other such that a cathode of the diode and an anode of the DC power supply are each arranged on the anode side of the light emitting element, and 
 the current detector detects the existence of an electric current on the parallel electric path in a period when an electric current is instantaneously interrupted by the instantaneous current interruption circuit. 
 
     
     
       2. The light emitting element failure detector according to  claim 1 , wherein the instantaneous current interruption circuit comprises
 a switcher that switches between supplying and stopping an electric current from the constant current circuit to the light emitting element, and 
 a switch controller that controls switching of the switcher. 
 
     
     
       3. A light emitting element failure detector that detects a short-circuit of a light emitting element in a light emitting element circuit that includes the light emitting element, a current supply path to the light emitting element, a constant current circuit that supplies an electric current to the light emitting element via the current supply path, and an electric discharge path that discharges an electric charge accumulated at the light emitting element and at a region connected between both electrodes of the light emitting element when the constant current circuit stops a current supply to the light emitting element, the light emitting element failure detector comprising:
 an instantaneous current interruption circuit that is arranged on the current supply path different from the electric discharge path and that instantaneously interrupts an electric current that the constant current circuit supplies to the light emitting element, and 
 a parallel electric path connected to the light emitting element in parallel between an anode and cathode of the light emitting element, the parallel electric path being different from the electric discharge path, wherein 
 the parallel electric path comprises
 a diode, 
 a DC power supply that generates a direct current reference voltage having a positive value lower than a voltage between the anode and cathode of the light emitting element in a normal state, in which the direct current reference voltage is applied to the light emitting element via the diode, and 
 a current detector, wherein 
 
 in the parallel electric path, the diode, the DC power supply, and the current detector are connected to one another in series, and the diode and the DC power supply are connected to each other such that a cathode of the diode and an anode of the DC power supply are each arranged on the anode side of the light emitting element, and 
 the current detector detects the existence of an electric current on the parallel electric path in a period when an electric current is instantaneously interrupted by the instantaneous current interruption circuit, 
 wherein the instantaneous current interruption circuit comprises
 a switcher that switches between supplying and stopping an electric current from the constant current circuit to the light emitting element, and 
 a switch controller that controls switching of the switcher, 
 
 wherein 
 the light emitting element circuit further comprises a PWM signal generator that sets a pulse width based on a set dimming level and generates a PWM signal comprising a pulse train having the set pulse width, a drive circuit that receives the PWM signal generated in the PWM signal generator and outputs a PWM control signal comprising a pulse train having the same pattern as the pattern of the PWM signal, and a current-controlling switch that is arranged on the current supply path, to which the PWM control signal is input, and switches supplying and stopping of an electric current to the light emitting element by the PWM control signal, 
 the PWM signal generator generates the PWM signal by removing at least one pulse in succession from the pulse train at a predetermined cycle and supplies the generated PWM signal to the drive circuit, 
 the current-controlling switch arranged on the current supply path different from the electric discharge path serves as the switcher, and 
 the PWM signal generator and the drive circuit serve as the switch controller by setting a period of absence of a pulse due to removal of the pulse in succession to the instantaneous interruption period of an electric current. 
 
     
     
       4. The light emitting element failure detector according to  claim 3 , wherein the PWM signal generator selects the number of pulse which is removed in succession based on the set pulse width and the instantaneous interruption period which is set in advance. 
     
     
       5. The light emitting element failure detector according to  claim 1 , wherein the light emitting element is an organic EL element. 
     
     
       6. The light emitting element failure detector according to  claim 1 , wherein the light emitting element is an LED element. 
     
     
       7. A light emitting element failure detection method that detects a short-circuit of a light emitting element in a light emitting element circuit that includes the light emitting element, a current supply path that supplies a current causing the light emitting element to emit light, a constant current circuit that supplies an electric current to the light emitting element via the current supply path, and an electric discharge path that discharges an electric charge accumulated at the light emitting element and at a region connected between both electrodes of the light emitting element when the constant current circuit stops a current supply to the light emitting element, the light emitting element failure detection method comprising:
 an instantaneous current interruption step in which, on the current supply path different from the electric discharge path, an electric current that the constant current circuit supplies to the light emitting element is instantaneously interrupted, and 
 a current detection step in which the existence of an electric current on a parallel electric path, the parallel electric path being different from the current supply path and from the electric discharge path, in a period is detected when an electric current is instantaneously interrupted in the instantaneous current interruption step, in a state in which a diode and a DC power supply that generates a direct current reference voltage having a positive value lower than a voltage between the anode and cathode of the light emitting element in a normal state, in which the direct current reference voltage is applied to the light emitting element via the diode, are connected to each other, and in the parallel electric path connected to the light emitting element in parallel between the anode and cathode of the light emitting element, the diode and the DC power supply are connected to each other such that a cathode of the diode and an anode of the DC power supply are each arranged on the anode side of the light emitting element.